1. Technical Field
The present invention relates to a technique to eject fluid from an ejection head.
2. Related Art
An inkjet printer configured to print an image by ejecting ink on a printing medium is now widely used as an image output apparatus because printing of high-quality images is easily achieved. Also, by ejecting various type of fluid prepared to have adequate components (for example, liquid including fine particles of functional materials dispersed therein or semifluid such as gel) instead of the ink on a substrate using this technique, manufacturing of various types of precision components such as electrodes, sensors, and biochips is considered to be easily achieved.
In the technique as described above, a specific ejection head provided with fine ejection ports is employed so as to enable ejection of fluid of accurate amount to an accurate position. The ejection head is provided with driving elements (for example, a piezoelectric element) connected to the ejection ports, and the fluid is ejected from the ejection ports by supplying a driving voltage waveform to the driving element. The amount or the shape (for example, the size of liquid drops) of fluid to be ejected from the ejection ports can be changed by controlling the driving voltage waveform to be applied to the driving element.
When an amplifier element such as a transistor for generating the driving voltage waveform, there arise problems such as power consumption due to dissipation in the amplifier element (for example, collector dissipation of the transistor) or upsizing of the device due to the necessity of a heat discharging panel for releasing heat generated by the power consumption. Accordingly, a technique to generate the driving voltage waveform without using the amplifier element by providing a plurality of power sources having voltages different from each other and changing the voltage by switching these power sources as needed is proposed (JP-A-2003-285441).
However, with the proposed technique, although high power efficiency is achieved, there is a problem of difficulty in generating an accurate driving voltage waveform. In other words, since the power efficiency is enhanced by switching the power sources, the generated driving voltage waveform assumes a stepped waveform in which the voltage is changed in a staircase pattern, so that output of an accurate waveform is difficult. However, when the driving voltage waveform is generated using the amplifier element such as the transistor, the electric power is consumed by the amplifier element, and hence the power efficiency is lowered.